Introduction To Hibernate Interview Questions And Answer
Hibernate is an object mapping tool it helps to simplify the connection of application with database.it provides the mapping of java object with database tables means It maps the java class with the table in the database. Name of the table and class depends upon the developer choice of the developer .it has a feature to give name according to the requirement of the business. It smooth database connectivity of the application. Hibernate also provides database independent query language which is known as HQL – hibernate query language. it is an object-oriented version of SQL language this helps the application to easily migrate with other databases in case of change of the database in the future time.
Hibernate also provides lots of other features like automatic table creation this is one of the most powerful features of hibernate. To support this only we have to do small configuration in XML file after that everything takes care by the hibernate only. Hibernate do dirty checking means it always checks the state of the Java object if it finds any changes in the state of the object it does update the database automatically. it has second level catch atomically enabled which helps to improve the performance of the application. These are the powerful features of Hibernate.
Now, if you are looking for a job which is related to Hibernate then you need to prepare for the 2019 Hibernate Interview Questions. It is true that every interview is different as per the different job profiles. Here, we have prepared the important 2019 Hibernate Interview Questions and Answers which will help you get success in your interview.
Below are the 10 important Hibernate interview questions and answers that are frequently asked in an interview. These questions are divided into two parts are as follows:
Part 1 – Hibernate Interview Questions (Basic)
This first part covers basic Hibernate Interview Questions And Answers.
1) Differentiate between get and load in Hibernate?
Answer:
Get method hits the database always if it does not found a cached object. It gives a completely initialized object which may involve several databases calls this may degrade the performance the application, While load method may return the proxy object if an object is not cached it hits the database for all methods of the object except the getId() method. If an object does not found anywhere get method return the null value while load method will throw the exception ObjectNotFoundException. So we can use these methods as per our requirements.
2) What is the difference between, persistent, transient and detached object?
Answer:
In Hibernate, There are 3 states of the Object given below.
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These are transient, persistent, detached. Any object will be in persistence state if it is associated with Hibernate session. any change in the current object will be reflected in the database based on our flush strategy. Automatic flush happens whenever any property of object change or explicit flushing by calling flush() method of Session class In case of an instance which was earlier associated with some persistent context but now it is no longer associated, it is detached state.
Let us move to the next Hibernate Interview Questions.
3) Is it Can possible to make a Hibernate Entity Class final?
Answer:
Yes, it is possible to make a Hibernate Entity class final, but it is not a good practice. Because Hibernate uses a proxy pattern for performance improvement of application and in the case of the lazy association, by making an entity class as final, Hibernate will no longer be able to use a proxy, a reason behind it is Java doesn’t allow extension of the final class; it limits the performance improvement options. Though, we can solve this problem if our persistent class is an implementation of an interface, which declares all public methods defined in the Entity class.
4) Explain the query cache?
Answer:
This is the common Hibernate Interview Questions asked in an interview. Query Cache is used to store the result of the SQL query for future calls for performance improvement. It can also be used along with a second level cache of hibernate to improve the performance of the application. Hibernate has many open source caching solution to implement Query cache.
5) Why it is must to provide no argument constructor in Entities?
Answer:
Entity class must contain a no argument constructor, because Hibernate framework creates an object of these classes using Reflection API, by calling new Instance() method of the Class class. Instantiation Exception will be thrown by this method if it doesn’t found any argument constructor inside Entity class.
Part 2 – Hibernate Interview Questions (Advanced)
Let us now have a look at the advanced Hibernate Interview Questions.
6) Explain the Session’s lock() method in Hibernate?
Answer:
Session class’s lock() method is used to reattach object without updating or synchronizing with the database. So we need to be very careful while using this method. We can always use update() method to sync with the database during reattachment.
7) Explain Second-level Cache in Hibernate?
Answer:
Second-level Cache is maintained at Session Factory level and used to improve the performance of the application by saving few database round trip. It is also available to the whole application rather than any particular session
Let us move to the next Hibernate Interview Questions.
8) What the benefits are of hibernate over JDBC?
Answer:
Hibernate can be used with any type of database because it is database independent while In JDBC, Developer has to write database specific queries.
In hibernate, we don’t need to be an expert of writing complex type of queries, because HQL ease query writing process while in case of JDBC, a developer has to write and tune queries.
In hibernate, there is no need to create connection pools because hibernate does all connection handling automatically In JDBC, connection pools need to be created by developer
9) In how many ways objects can be identified and What are the different fetching ways in Hibernate?
Answer:
This is the most Frequently asked Hibernate Interview Questions in an interview. For the Object identification, three ways are there listed below.
Using database identity: Relational database objects can be identified if they represent the same row.
Using Object Equality: Using equals() method.
Using Object Identity: Using == operator.
Following are the fetching strategies available in hibernate:
Batch Fetching
Join Fetching
Sub-select Fetching
Select Fetching
10) Tell the few interfaces name of Hibernate framework?
Answer:
Session Factory: it is an immutable thread-safe cache of compiled mappings for a single database. We have to initialize it once, then we can cache and reuse it. its instance is used to get the Session objects for various database operations.
Session it is a single-threaded, short-lived object representing an interface between the application and the persistent store. It wraps JDBC java.sql.Connection and works as a factory for Transaction. You should open a session only when it’s required and close it as soon as you are done using it. A session object is the interface between java application code and hibernate framework and provide various methods for CRUD operations in Java.
Transaction): it is a single-threaded, short-lived object used by the java application to specify atomic units of work. It abstracts the application from the underlying JTA transaction or JDBC. A Session might contain multiple Transactions in some cases.
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